Conventionally, as an electric motor of this kind, one disclosed in Patent Literature 1 is known. The electric motor is a so-called rotating machine, and includes a first rotor and a second rotor which are connected to a first rotating shaft and a second rotating shaft, respectively, and a single stator. The first and second rotating shafts are arranged concentrically with each other, while the first rotor, the second rotor and the stator are arranged in the direction of radius of the first rotating shaft from inside in the mentioned order.
The first rotor includes a plurality of first permanent magnets and second permanent magnets which are arranged in the circumferential direction, respectively. The first and second permanent magnets are arranged in parallel with each other in the direction of axis of the first rotor. The stator is configured to generate a first rotating magnetic field and a second rotating magnetic field which rotate in the circumferential direction. The first rotating magnetic field is generated between the stator and a portion of the first rotor toward the first permanent magnets, and the second rotating magnetic field is generated between the stator and a portion of the first rotor toward the second permanent magnets. The second rotor includes a plurality of first cores and second cores which are arranged in the circumferential direction, respectively. These first and second cores are comprised of soft magnetic material elements. The first cores are arranged between a portion of the first rotor toward the first permanent magnets and the stator, and the second cores are arranged between a portion of the first rotor toward the second permanent magnets and the stator. The numbers of the magnetic poles of the first and second permanent magnets, the numbers of the magnetic poles of the first and second rotating magnetic fields, and the numbers of the first and second cores are set to be equal to each other, respectively.
In the electric motor arranged as described above, as the first and second rotating magnetic fields are generated by the supply of electric power to the stator, the first and second cores are magnetized by the magnetic poles of the first and second rotating magnetic fields and the magnetic poles of the first and second permanent magnets, whereby magnetic force lines are generated between these elements. Further, the first and second rotors are driven by action caused by the magnetic forces of the magnetic force lines, and in turn power is output from the first and second rotating shafts.
In the above-described conventional electric motor, due to the arrangement thereof, to cause the magnetic forces of the magnetic force lines to properly act so as to convert electric power supplied to the stator to power and output the power from the first and second rotating shafts, not only a first soft magnetic material element row comprised of the plurality of first cores but also a second soft magnetic material element row comprised of the plurality of second cores are indispensable, and it is inevitable to result in an increase in the size of the electric motor, and an increase in the manufacturing costs thereof. Further, due to the arrangement thereof, the electric motor is only possible when there holds speed relationship in which the difference between the rotational speed of the first and second rotating magnetic fields and the rotational speed of the second rotor, and the difference between the rotational speed of the second rotor and the rotational speed of the first rotor become equal to each other. This degrades the degree of freedom in design of the electric motor.
The present invention has been made to provide a solution to the above-described problems, and an object thereof is to provide an electric motor which is capable of reducing the size and manufacturing costs thereof while enhancing the degree of freedom in design of the same.
[Patent Literature 1]
Japanese Laid-Open Patent Publication (Kokai) No. 2008-67592.